This invention relates to method and apparatus for quenching ferrous and non-ferrous tubular members and, more particularly, to an apparatus and method for the high speed quenching of tubular members at approximately uniform cooling rates on the inside and outside surfaces while minimizing deformation thereof.
The invention is particularly applicable to quenching, in a steel mill environment, heavy-walled steel pipe to produce a relatively uniform martensitic structure throughout and will be described with particular reference thereto. However, it will be appreciated by those skilled in the art that the invention has broader application and may be used to cool any heated cylindrical member in a relatively uniform manner.
Heat treating long lengths of steel pipe or tubular members had long presented a problem for the steel mill industry and a number of different approaches have been used to address this problem with varying degrees of success. In the conventional heat treat process, the tubular member is heated to a temperature above the austenitic temperature to achieve the necessary phase transformation throughout the tubular member and the tubular member is then cooled at a rate at least equal to the critical cooling curve to produce a martensitic structure which is sufficient to result in the desired hardness. The inherent problem for many pipe applications requiring through hardening is to quench the tubular member in such a fashion that a relatively uniform martensitic grain structure is produced throughout the wall cross-section of the tubular member. If the inside and outside surfaces of the tubular member are not cooled at a sufficient rate, then the martensitic structure will only occur on the inside and outside external surfaces and possibly not in the interior of the wall section. As is conventionally known, the volume expansion resulting from the non-uniform martensite transformation will tend to produce cracks at the exterior surfaces and dimensionally distort the tubular member, the distortion occurring either in the roundness, the straightness, and/or surface markings on the tubular member. The problem as thus explained is particularly compounded for heavy walled pipe where through quenching is difficult to achieve and, in many applications, require the addition of expensive alloys, to shift the knee of the continuous cooling transformation curve so that the desired martensitic structure can be produced.
Various quench arrangements have been heretofore used which have as their objectives, fast quenching rates with minimal distortion tendencies. U.S. Pat. No. 3,671,028 to Klaus Hemsath and assigned to the present assignee discloses an outside quench system which utilizes a plurality of jet nozzles positioned in an annular array to effect a highly efficient heat transfer cooling rate (using "fresh" as contrasted to "spent" quench liquid) on the outside surface of the pipe in a pass-through quench system. Certain aspects of the '028 patent are utilized in this invention and the '028 patent is hereby incorporated by reference. However, the system disclosed in the '028 patent is directed only to quenching the outside surface of the pipe and is not applicable to those applications where the pipe has significant wall thickness. Also, the quench mechanism of the '028 patent is a "pass-through" type, which progressively cools only portions of the tubular member as the tubular member is longitudinally moved or passed through the quench. Thus, there are inherent problems resulting from the adverse effects of cooling, by conduction, the still hot portion of the pipe outside the quench vis-a-vis that portion of the pipe which is inside the quench which limit the suitability of the quench arrangement to certain applications.
Several arrangements for simultaneously quenching the inside and outside surfaces of a tubular member have been utilized with some success. U.S. Pat. Nos. 4,116,716 to Itoh et al and 3,997,375 to Franceschina et al typify such approaches. In these arrangements, the tubular member is immersed in a cooling tank and a nozzle is inserted into the tubular member at one end thereof. The bath cools the ouside surface of the tubular member while the water from the nozzle cools the inside surface. When the tubular member, however, is immersed in the tank, a steam vapor barrier is immediately produced at the surface of the tubular member which inhibits a fast cooling rate. The cooling along the inside surface of the tubular member by means of a nozzle would be faster than that at the outsi e pipe surface limiting the applications of the quench and tending to deform the tubular member for reasons noted above.
Recognizing the limitations of the cooling tank quench, a number of "pass-through" quench arrangements have been used which employ a lance-mandrel arrangement for the interior spray nozzle to cool the inside of the pipe and various radially directed nozzle or radial flow arrangements for cooling the outside surface of the tubular member. U.S. Pat. Nos. 4,417,928 to Heine et al, and 4,490,187 to Krupport illustrate various arrangements using this approach. However, all of such arrangements described must employ complicated support structures for suspending the lance within the interior of the pipe as it longitudinally travels along the lance's axis. In addition, since all such arrangements use a pass-through technique, there is a progressive cooling of the pipe with the attendant deformation problems resulting therefrom as noted above. The problem is further aggravated because the quench liquid from the interior nozzle passes through the tubular member before the entire outside surface of the pipe is cooled by the quench mechanism. Furthermore, the radially-inwardly directed nozzles used to cool the outside surface of the tubular member are spaced from one another a considerable distance (in a relative sense). This spacing creates a steam barrier or stagnation region between longitudinally adjacent nozzles which inhibits cooling and promotes metallurgical non-uniformity properties in the pipe (and thus deformation) even though any particular stagnation zone is, within a short time, removed as the pipe's movement places the zone under the full force of the jet. To reduce the size of the stagnation zones to workable limits, the pressure of the nozzles must be increased, typically to about 100 psi to create sufficient turbulence at the pipe surface to reduce the stagnation zone areas. This in turn, increases the sizing of the pumps and other system components and the energy requirements of such systems than that which otherwise may be required.
This feature is accomplished in a quench arrangement rotating the tubular member about its longitudinal axis while maintaining the member in a longitudinal stationary position; directing along generally tangential axes relative to the O.D. of the member a plurality of liquid cooling jet streams circumscribing the tubular member, the streams also being located at spaced intervals along the longitudinal axis and removed from the outside surface of the member so that the entire outside surface of the member along its longitudinal axis is engulfed engulfed and cooled by the cooling liquid emanating from the tangential jet streams; and, directing into the member along its longitudinal axis and from one end thereof a solid liquid cooling jet stream whereby the entire inside surface of the member is in complete contact with and cooled by the cooling liquid emanating from the longitudinal jet stream. Because the tubular member is rotated about its longitudinal axis while the member is in a longitudinally stationary position, the quench arrangement of the present invention subjects the tubular member to cooling along its entire length, thus removing the objectionable features of the pass-through quench system discussed above. The rotation of the tubular members which minimizes pipe bow is a achieved by drive roller units. A plurality of O.D. quench supply means spaced at intervals along the tubular member's longitudinal axis and encircling the member is then provided for cooling the outside surface of the tubular member. Each O.D. quench supply means includes a plurality of jet spray nozzles spaced longitudinally and circumferentially about the tubular member at a distance removed from the outside surface of the member with the axis of each jet spray nozzle oriented in a generally tangential direction to the O.D. of the tubular member so as to produce a jet stream of cooling liquid to efficiently cool the outside surface of the pipe at a fast rate with minimal pressure. An I.D. quench supply means including a jet spray nozzle positioned at one end of the tubular member having an axis generally in line with the horizontal axis of the tubular member is provided for cooling the inside surface of the tubular member at approximately the same cooling rate as the O.D. quench supply means.
In accordance with another aspect of the invention, high heat transfer coefficients can be achieved at the outside surface of the tubular member. The tangential jet streams are directed to oppose the direction of rotation of the tubular member to increase the velocity of the cooling liquid relative the surface of the tubular member. In this manner, a swirling mass of "fresh" liquid coolant is placed in excellent heat transfer relationship with the outside surface of the tubular member.
In accordance with yet an other aspect of the invention, bending of the tubular member is minimized by controlling the rotational speed of the member such that tubular members having large diameters are rotated at slower speeds than tubular members having smaller diameters. Additionally, the rotation of the tubular member prevents circumferential temperature gradients from occurring about the inside surface of the pipe when quenching by means of the I.D. quench nozzle. Such temperature gradients could adversely effect the metallurgical properties at the inside surface and deform the tubular member.
In accordance with yet another important aspect of the invention, the quench mechanism is constructed to provide a simple and highly efficient method for processing steel pipe in a steel mill. The pipe is simply conveyed from the reheat furnace to a waiting position whereat it is laterally moved into the quench mechanism in a quench position, and after the tubular member is quenched, it is laterally moved to a removal position whereat it is conveyed away from the quench mechanism. This is achieved through the design of the O.D. quench supply means which include first and second quench supply manifolds for carrying cooling liquid therein, with each manifold having a top and bottom closed end and pivot means for bringing the closed ends of each manifold into close proximity with one another in a quench position so that both manifolds together, circumscribe the tubular member and then actuating the pivot means to move the top ends of the quench supply manifolds away from one another when the quench is in the transfer position to permit the tubular member to be lifted from the quench and moved to the removal station. The quench supply manifolds in turn carry the spray headers which in turn carry the tangentially directed spray nozzles for directing the jet streams in a swirling mass about the outside surface of the tubular member. This heat transfer relationship is achieved along the outside surface of the tubular member over the entire length of the tubular member by providing within each O.D. quench supply means a plurality of the tangential jet streams longitudinally spaced in close proximity to one another throughout the entire length of each O.D. quench supply means. This spacing precludes the formation of any significant stagnation zone between adjacent swirling masses of liquid coolant thus permitting even, uniform heat transfer (and thus metallurgical properties) without significant deformation over the entire length of the tubular member. It has been determined that high heat transfer coefficients can be achieved in the present invention with low nozzle pressures, typically in the order of 20 psi, thus resulting in a reduction of the energy requirements for the present invention while reducing the capital costs for the system when compared to the high pressure requirements of prior art quench systems.
In accordance with still another aspect of the present invention, a wide variety of pipe sizes can be accommodated within the quench arrangement of the present invention by providing adjustable idler roller means associated with each O.D. quench supply means to maintain, notwithstanding the diameter of the pipe, the horizontal axis of the tubular member in a centered position within the circular array of tangentially directed nozzles. The tangentially directed nozzles are also adjustable by rotation of the supply headers about their longitudinal axes so as to maintain a tangential arrangement between the jet spray axes and the O.D. of the tubular member.
In accordance with yet another aspect of the present invention, a simple four-bar link mechanism gently lifts, laterally moves, and gently sets down the tubular members with little rotation about its vertical axis to minimize any upset to the tubular member. The four-bar mechanism permits one tubular member to be transferred from the furnace discharge conveyor to the quench station while simultaneously transferring another tubular member from the quench station to the removal station to achieve fast and efficient processing of pipe through the mill. By counterbalancing the driving links of the four-bar link the power requirements for this transfer device are minimized. The design of the four-bar linkage provides for continuous rotation as opposed to a reversing motion of the four-bar linkage to further enhance the speed of the pipe processing time in the mill.
In accordance with still another feature of the present invention, and while it is contemplated that both the I.D. and O.D. quench supply means would operate to produce the same cooling rates at both the inside and outside surfaces, the quench arrangement could, depending on the service application requirements for the tubular member, be operated with I.D. quench supply means inoperative so that only the outside surface of the tubular member is quenched or the O.D. quench supply means could be inoperative so that only the inside surface of the tubular member is quenched or the flow rates between the I.D. and O.D. quench supply means controlled at some ratio to impart desired metallurgical properties to the tubular member. In this way, a heavy duty quench arrangement could easily function in an efficient manner for a wide variety of pipe heat treatments.
It is thus the principal object of the present invention to provide a method and apparatus for cooling tubular members to produce uniform metallurgical properties in the member while minimizing the tendency of the member to bow.
It is another object of the invention to provide an apparatus and method for simultaneously cooling the inside and outside surfaces of the tubular member at high cooling rates by minimizing the adverse effects of coolant vapor.
It is another object of the present invention to provide a quench system which permits, by virtue of its inherent capability to achieve high cooling rates, satisfactory quenching of pipe having heavier walls for any given steel composition when what was otherwise heretofore possible or, alternatively, to use lesser amounts of alloy additions to steels for quenching a given pipe wall thickness than what was otherwise heretofore possible.
Yet another object of the present invention is to provide an efficient and fast quench arrangement which permits the tubular members to be quenched in a longitudinally stationary position made possible by utilizing the "clam shell" configuration of the O.D. quenching means in combination with a walking arm mechanism for charging and discharging the tubular members.
It is yet another object of the present invention to eliminate the potential for prequenching a tubular member due to water dripping from nozzles in prior art devices which direct radial coolant streams against the outside surface of the tubular member.
Yet a still further object of the present invention is to provide a quench system which varies the rotation of the tubular member about its longitudinal axis to minimize bowing while simultaneously minimizing the formation of cooling vapor about its inside surface to enhance the cooling rate of the tubular member's inside surface.
It is a still further object of the present invention to provide a quench arrangement which, by virtue of its configuration, can satisfactorily quench a large number of different length pipes and which is easily adjustable to quench a wide variety of pipe diameters.
It is yet another object of the present invention to provide a quench arrangement which is relatively inexpensive to construct and operate.
it is a still further object of the present invention to provide a quench arrangement which can be selectively operated to cool either the outside surface or the inside surface of long tubular members independently or dependently of one another.
Still further advantages of the invention will become apparent to those of ordinary skill in the art upon a reading and understanding of the following description of the preferred embodiment.